The development of photonic devices with tailor-made optical properties requires the control and the manipulation of
light propagation within structures of different length scales, ranging from sub-wavelength to macroscopic dimensions.
However, optical simulation at different length scales necessitates the combination of different simulation methods,
which have to account properly for various effects such as polarization, interference, or diffraction: At dimensions much
larger than the wavelength of light common ray-tracing (RT) techniques are conveniently employed, while in the subwavelength
regime more sophisticated approaches, like the so-called finite-difference time-domain (FDTD) technique,
are needed. Describing light propagation both in the sub-wavelength regime as well as at macroscopic length scales can
only be achieved by bridging between these two approaches.
In this contribution we present on the one hand a study aiming at the determination of the intermediate size range for
which both simulation methods are applicable and on the other hand an approach for combining classical ray-tracing
with FDTD simulation in order to handle optical elements of large sizes. Generally, the interface between RT and FDTD
is restricted to very small sample areas. Nevertheless, many real world optical devices use e.g. diffractive optical
elements (DOEs) having comparably large areas in the order of 1-2 mm² (or larger). Therefore, one has to develop
strategies in order to handle the data transfer between FDTD and RT also for structures of such larger size scales. Our
approach in this regard is based on the symmetries of the structures. In this way support programs like e.g. MATLAB
can be used to replicate the near-field of a single structure and to merge it to the near-field of a larger area. Comparisons
of RT and FDTD simulations in the far-field can be used to validate the physical correctness of this approach. With such
procedure it is possible to optimize light propagation effects at both the macro- and microscale and to exploit their whole
potential for the manipulation and optimization of optical and photonic devices.